Relatively movable coils in slotted cores



May 7, 1968 J. A. MAASS 3 5 RELATIVELY MOVABLE COILS IN SLOTTED CORESFiled July 6, 1966 INVENTOR, JOACHIM A. MAASS United States Patent3,382,472 RELATIVELY MOVABLE COILS IN SLOTTED 'CORES Joachim A. Maass,3212 Querns Road, Belmar, NJ. 07719 Filed July 6, 1966, Ser. No. 563,6526 Claims. (Cl. 336-119) ABSTRACT OF THE DISCLOSURE A transformer with aninductive coupling coefficient that is adjustable over a wide rangehaving two ferromagnetic bases with each base having a surface with theslot and a wire disposed in each slot. The surfaces are held in abutmentand rotating the surfaces with respect to each other varies the couplingcoefiicient between the wires in the slots.

The present invention relates to transformers and more particularly totransformers with an adjustable inductive coupling coefiicient.

When the flux field of one inductance coil is linked with the turns ofanother inductance coil, the coils are considered to be inductivelycoupled. The effect of the coils on each other is called the mutualinductance. If one of the coils has an inductance L and the other has aninductance L the maximum value of mutual inductance has beentheoretically calculated as /L L In actuality this maximum has not beenobtained and, accordingly, it has been useful to describe the ratio ofactual mutual inductance, M, of two coils to the theoretical maximumVIE; as the coefficient of coupling, k, which is expressed by theformula w LlLz As the actual mutual inductance increases, the value ofthe coefficient of coupling approaches 1. In practice, couplingcoefiicients larger that .33 have not been obtained for mutualinductance with air core transformers or .5 in the case of powered-ironcore transformers. Overlapping windings have been used to achieveslightly higher coupling coeflicients. The difiiculty in obtaining alarge cou pling coefiicient is due to the fact that the coils includingthose wound on the same coil form, produce flux fields which are notentirely common to the conductors of which the inductance coils aremade.

In the past, values of mutual inductance of .5 or slightly higher havebeen acceptable for most uses. However, the increase in the number andkind of devices employing double tuned filters such as broad band if.amplifiers have presented a need for inductive couplings by means ofcoils with very small inductance values and large adjustablecoefficients of coupling. The present invention fulfills this need.

An object of this invention is the provision of an inductive couplingwith an adjustable coefiicient of coupling.

Another object is to provide an adjustable inductive.

coupling with a wide range of coupling coefiicient values including veryhigh coupling coefficients.

A further object is the provision of a high mutual inductance betweenelements with small inductive values.

Still another object is to provide a transformer that is easy toconstruct and adjust.

The exact nature of this invention as well as other objects andadvantages thereof Will be readily apparent from consideration of thefollowing specification relating to the annexed drawing in which:

FIG. 1 is an exploded view, partly in section, of a preferred embodimentof the invention;

FIG. 2 illustrates an exploded view, of a modification of the invention;and

FIG. 3 shows an exploded view, partly in section, of yet anothermodification of the invention.

Referring now to the drawings wherein like reference charactersdesignate like or corresponding parts throughout the several views,there is shown in FIG. 1 (which illustrates a preferred embodiment)first and second ferromagnetic bases 11, 12, illustrated as circulardiscs, said bases being rotatably mounted on shaft 13 so that they abuteach other and can be rotated with respect to each other. Base 11 isprovided with a pair of holes 14, 15, and base 12 with a correspondinglyaligned pair of holes 16, 17. Arc shaped recesses or slots 18', 19,extend between the ends of the holes on the mutually opposing sides ofthe bases 11 and 12, respectively, the slots also being mutuallyaligned. In base 11, wire 20 passes through hole 14, along slot 18 andthrough hole 15 to form one of the coils in the transformer. The othercoil is formed in base 12 by wire 21 which passes through hole 16, alongslot, 19 and through hole 17 so as to make the two coils mirror imagesof each other when directly opposed. In this position practically all ofthe magnetic field that could be produced by one or both of the wireswill be confined in the ferromagnetic material in such a manner that theflux field will be almost completely common to both coils therebyyielding a high mutual inductance. As the bases are rotated with respectto each other the portion of the coils opposing each other, andtherefore sharing the same field, decreases thereby decreasing themutual inductance and coeflicient of coupling. If the relative rotationis continued until no portion of the two coils are overlapping, theferromagnetic material then acts to prevent the two fields from beingcommon thus providing a coefficient of coupling that is substantiallyzero.

It is apparent that extra turns may be added as necessary and that morethan one coil may be mounted on each base. FIG. 2 shows an embodimentwherein wire 20 in base 11 is provided with a plurality of turns andwire 22 is also wound to provide an additional inductance coil. Wires 21and 23 are shaped on base 12 to provide mirror images of coils made byWires 20 and 22, respectively, when directly opposed. Additional holesand slots may be provided as necessary.

In some cases it is not possible to wind the necessary plurality ofturns as shown in FIG. 2. Another embodiment, providing for more turnsin the wire, is shown in FIG. 3. In this embodiment, slots 18 and 19comprise parallel straight slot sections connected at their ends by arcshaped slot sections whose concave side face each other. A plurality ofturns may be wound in slot 18 with a mirror image of the coil (notshown) formed in base 12. Mutual inductance can be lowered to almostzero by rotating the bases so that the straight portions of slots 18 and19 are perpendicular to each other. The mutual inductance will be loweven though the oppositely disposed coils are not shielded from eachother by the bases because of the orthogonally arranged lines of force.

Various modifications may obviously be resorted to by those skilled inthe art without departing from the spirit and scope of the invention, ashereinafter defined disposed in said slot in said second base, and meansfor holding the slotted surfaces of said bases in abutment and forsubstantially confining said first and second wires in ferromagneticmaterial, said means including means for allowing movement of saidsurface and slot of one of said bases relative to said surface and slotof the other of said bases, said slots being positioned such thatrelative movement of said surfaces varies the alignment and inductivecoupling coefficient between said first and second wires.

2. The device as claimed in claim 1 and wherein said first and secondbases each include at least two holes therethrough and the ends of thefirst wire pass through the holes in said first base and the ends of thesecond wire pass through the holes in said second base.

3. The device as claimed in claim 1 and wherein the slot and wire insaid first base is a mirror image of the slot and wire in said secondbase when directly opposed- 4. The device as claimed in claim 1 andwherein the slots in said first and second bases each have parallelstraight portions connected at their ends by arcuate por tions.

5. The device as claimed in claim 4 and wherein the first and secondwires each comprise a plurality of loops.

6. The device as claimed in claim 5 and wherein the recess and wire insaid first base is a mirror image of the recess and wire in said secondbase when directly opposed.

References Cited UNITED STATES PATENTS 2,894,231 7/1959 Krasno 336 X2,900,612 8/1959 Tripp 336123 2,921,280 1/1960 Litwin et a1. 3361203,090,933 5/1963 Henry-Baudot 336-120 3,179,909 4/1965 Cheney 336-120FOREIGN PATENTS 224,976 1924 Great Britain.

DARRELL L. CLAY, Primary Examiner.

T. I. KOZMA, Assistant Examiner. I

